The present invention relates to a method of closing hose or bag shaped packings, primarily foodstuff packings, whereby a constricted portion of the packing is clamped by a ring shaped non-metallic clamp binder, which is caused to be narrowed about the constriction by a closing pressure applied from opposite sides thereof and is fixed in its shape as attained when it is subjected to a closing pressure.
Typical packings will be sausage articles, which have a porous sausage skin of a fibrous material, and bag or sausage shaped packings for other kinds of foodstuffs, e.g. soups, the packing material here being a tight, tubular plastic sheet material. The sausage skin materials are porous because the products should be subjected to a smoking treatment, whereby they are given both a desired taste and a long durability, while the plastic sheet material should be as tight as possible for rendering the packed products as durable as possible.
In both cases almost the same problem exists, namely that the binding of the constrictions should be effected very tightly such that in case of sausages the clamp binders will not slide on the normally very slippery sausage skins before and during the smoking, while the clamps when mounted on the plastic sheet envelopes should likewise be non-slidable, but also provide for an effective sealing against penetration of air. In both cases it is normally necessary to make use of clamping forces which are so high that a potential danger of the sheet material being damaged will exist, and, in fact, it is well known that in the relevant productions a most significant waste on this account is being experienced.
For these types of bindings it has been customary, almost exclusively, to use binders of the metallic clip type, i.e. U- or C-shaped metal strips, which are introduced over a constriction area of the packing and bent by reasonably high clamping forces so as to be closed as a ring about the constriction. Much could be said about the advantages and disadvantages of these metal clips, but here it should just be mentioned that they are responsible for the high waste, because they have a limited ability to hold the material tightly clamped, and that they show a major disadvantage in just being of metal. Generally, according to modern standards, any kind of metal is unwanted in connection with foodstuff articles. It is relevant to mention also that it has been found that the metal clips are simply unable to close the plastic sheet packings with any particularly high degree of tightness, at least not without an associated highly potential danger of damaging the material so that the closure will be untight anyhow. Through the recent years several extremely tight plastic sheet materials have been developed for increasing the storage durability of the various foodstuff products, but it has been realized that these developments are in fact superfluous as long as the materials cannot be closed with the same high degree of tightness.
Already for leaving the use of metal there have been some attempts to make use of plastic binders, but the designs of these binders have not been suitable for use with large size packings, i.e. packings with relatively thick constriction areas. An advantage of the plastic binders, apart from their not being of metal, is that they may be provided with locking means such that they may be tightened about the constriction area and be fixed in a closed ring shape, whereby they may clamp the constriction area with high forces without these forces being limited by the ability of the binder material to retain a bent shape against return-bending forces from the clamped constriction area.
The already known plastic binders, however, suffer from various drawbacks which will not be discussed in great detail in the present context. Generally they are based on the same basic ideas as the metal clips, namely that they should serve to surround the constriction area with sufficient tightness to be non-slidingly secured and to provide a high degree of sealing of the constriction area. Most of the known plastic binders are unusable for large size packings because they comprise a U-shaped portion, the legs of which are received in a hole in an opposed counter portion, whereby the constriction material will be clamped against the edges of the receiver hole, and this may give rise to concentrated clamping forces which cause a rupturing of the sheet material.
There are not either, so far, any reports on plastic binders being applicable to effect any "super sealing" of the relevant constriction areas.
In connection with the invention a major problem has been found in the fact that it is in no way ideal to effect a binding of a constriction area by way of a circularly annular binder or a binder having major portions shaped in this manner. Experiments and calculations have shown that what happens is a peripheral compaction which forms a barrier against the clamping pressure being transferred to the inner portions of the constriction area. When a high pressure is applied the relatively thin layer of the compacted peripheral material will be axially displaced by flowing, but since the material is frictionally cohering with the inner material the latter will be axially drawn by such displacement and deformation of the outer material. This drawing is effected based on the resiliency of the nonflowing material, and it may well happen that by an applied high clamping pressure the inner material next to the material in the zone of flowing material will hereby be stretched beyond its so-called rupture prolongation, i.e. the material will burst.
The above considerations apply to casing materials of plastic, but similar considerations may apply to casings of fibrous material, and in both cases the result will be that in fact none of the known binders are optimal with respect to creating a high clamping pressure in a safe manner, i.e. without damaging the casing material.
The considerable waste should be seen on the background that apparently it has not earlier been realized what is really happening in the constriction area when a high clamping pressure is applied from binder portions of various configurations, and it is believed that the present invention represents a pioneer work in this respect. For the normal use of metal clips it is typical that some empiric tests are made at the beginning of a production, such that the waste can be held as low as possible and that an attempt to reduce the waste further by lowering the clamping pressure will only result in a similar or even worse waste, now not by rupturing the material but by the binders not being safely held on the casings. It is a traditional counter measure to mount two or more clips at each constriction, but the waste percentage will still be high, and as far as an extremely sealed closing is concerned such a series of clips will be of no help at all, as none of the clips will have any chance of providing for a "super sealing".
As will be apparent from the foregoing the main purpose of the invention is to provide a method and a binder which will enable the constrictions to be bound by a relatively high binding pressure with a very low risk of the constriction material being damaged, such that the waste can be reduced considerably or even be eliminated. Based on the same contribution it is a further purpose of the invention to provide a method and a binder which will be applicable for obtaining a "super sealed" closing of the constrictions, this of course also being of utmost importance.
According to the new concept of the invention it has been found that for a practically ideal relation between a high clamping pressure and a low risk of damaging the casing material the constriction area should be clamped between opposed surface portions of substantially straight clamping beams of the binder clamp and be caused to be compacted into a final shape, in which it is cross sectionally oblong in the longitudinal direction of the substantially parallel clamping beams, preferably with a length at least twice the distance between the clamping beams. Obviously the applied clamping pressure and the size of the binder should still be adapted to the particular production, but already with a conventional adaptation in this respect, i.e. by empirical selection of the conditions, the result will be a drastic reduction of the waste percentage, because with the said disposition of the constriction area between substantially parallel clamping beams a relatively very high clamping pressure can be applied without damaging the casing material.
The invention is based on advanced studies of the behaviour of the casings material in the constriction area when exposed to a clamping pressure, and it has even been found that it is possible to select a correct binder and clamping pressure based on the known basic or starting parameters of the process, i.e. the dimensions and material constants of the casing material, thus without relying solely on empirical tests. It is believed, however, that in the present connection it will be unnecessary to elucidate the theoretical basis of the invention when the result thereof can be expressed in terms of concise and novel method and design conditions.
Briefly, the physical effect of applying the clamping pressure between straight and parallel clamping beams will be that the clamping pressure is transferred to the inner material portions in the constriction area without being hindered by any compaction taking place lengthwise of the clamping beams as would occur along curved clamping means, and the clamping pressure, therefore, will be taken up by the constriction area in a relatively very "soft" manner involving no drastic differences in the behaviour of the different neighboring layers of the material in the constriction area. Correspondingly, the physical effect of the constriction area being elongated in the direction is that the degree of compaction of the constriction area will be relatively small, whereby it is ensured that the different material portions as frictionally engaging each other by the compression thereof will not give rise to substantial rubbing effects, such that the casing material is unlikely to be ruptured hereby.
The required clamping together of two opposed clamping beams to a desired final position is achievable with the use of clamping beams, which are essentially rigid or stiff, and which are interconnected endwise through tensile strong leg portions, of which at least one is adapted to be received in a receiver opening in the opposite clamping beam in a length variable and fixable manner. In any production there will be some variations in the general thickness of the constriction areas, and, consequently, the leg portion will intrude more or less in the receiver opening or even protrude more or less from the rear side of the opposite clamping beam. Correspondingly, in order to limit the number of different standard binders it may be desirable, for a given production, to select a binder type which will give rise to such rearwardly protruding leg ends, and generally this will be disadvantageous in that projecting binder portions will present a tearing risk towards neighboring packings. In the prior art, as far as plastic binders are concerned, the same problem has existed, though to a much higher extent because of the larger displacement of the leg portion during the clamping operation, and it has been suggested in that connection that the problem of the widely rearwardly projecting leg ends may be solved by simply cutting away these protruding portions immediately at the rear side of the binder portion from which they project. This, however, has turned out to be an unacceptable solution of the problem, because in connection with the production of foodstuff products it is highly unacceptable to have loose cut off binder portions occurring together with the products themselves.
With the present invention it is ensured that a given binder type having a specific length of the leg portion is usable in connection with an increased number of different products and their associated variations of the general thickness of the constriction areas, because with the oblong configuration of the clamped constriction area the intrusion or protrusion of the leg portion into or beyond the receiver opening will vary relatively little due to the associated small clamping displacement of the leg portion. It is practically possible, therefore, to entirely avoid the cutting of the leg portions by prescribing either the use of such a thickness of the receiver clamping beam that the end of the leg portion will remain inside the receiver opening despite the occurring thickness variations of the constriction areas or, where the leg members will protrude moderately from the rear sides of the receiving clamping beams, that the outer ends of the leg portions be smoothly rounded so that these end portions will not present any tearing risks. Hereby each standard binder type will be applicable for the binding of both a variety of different products and for the binding of standard products showing a low tolerance with respect to the general thickness of the constriction areas, without the end portions of the leg members having to be cut away.
While these results of the invention are highly important it may be still more important that the invention provides for a practical possibility of a "super sealed" closure to be obtained in a well defined and reproduceable manner. It has been found that the main condition of a super tight closure is in fact rather simple to formulate and to realize based on the principles of the invention, while at the same time it has been made clear why such a closure is otherwise practically unachievable.
In order to provide a full sealing all material portions across the constriction area should be pressed firmly together as well as firmly against the surrounding clamp. Inside the constriction area and on the surface thereof, due to wrinkles and foldings of the casing sheet, there will exist a plurality of unclosed narrow channels, which will not be closed merely by a pressure sufficient to force the sheet surface sub areas tightly together. In order to close these channels it is simply necessary to subject the material at each relevant place to such a high pressure that the plastic material is deformed, by a real deformation flowing, and because the wrinkles may occur all over the constricted area the condition of really producing a totally sealed closure will be that each and all sub portions of the constricted area are subjected to such a high deformation pressure without any portion thereof hereby being fractured.
The building up of such a high and non-damaging pressure even inside the central portion of the area is generally possible with the use of the method according to the invention, while with the use of the conventional metal clips there are several sub areas in which the pressure will be either too high or too low, or, in other words, it is impossible to avoid the situation that the pressure is suitable in some sub areas without being either too low or too high in other sub areas, whereby the result is bound to be unsuccessful.
Some of the already known plastic binders could be better suited for providing a less varying pressure in the constriction area, but here one problem is that the sheet material, as already mentioned, is forced against the edge of a hole so as to readily burst at this place by an applied high pressure, and another problem is that in the prior art it has generally been endeavored to produce a finally bound constriction area of approximately uniform thickness and width. It has now been found, both theoretically and experimentally, that a deformation pressure midways in the constriction area cannot in practice be built up without the remaining material being damaged, unless the thickness, i.e. the distance between the opposed clamping beams, is noticeably smaller than the width of the area. Likewise it is important that the binding is effected between substantially straight, opposed clamp portions.
In practice, in a given production, it should of course be ascertained that the clamping pressure is adjusted so as to be effective for the desired result to be obtained, i.e. high enough to cause an overall flowing deformation of the material, but without having caused damage to any part of the material. These functions cannot be directly observed, but test samples may be produced for being tested and inspected. The fulfilling of the conditions for obtaining a "super sealed" closure according to the invention can be verified by removing the clamp and broadening out the tubular casing material of the constriction and then (1) inspecting the material for observable fractures, and (2) measuring the sheet thickness all the way round to make sure that at every sub area the sheet material has undergone the deformation flowing, this being inherently connected with an axial displacement of the material and therewith with a permanent thickness reduction thereof. Thus, when the material is unbroken and is of reduced thickness all the way over the former constriction area, then the applied pressure has been correct and applied correctly for providing the super sealing effect, and the production may start or continue with the same mounting conditions for mounting the binders of the particular selected type.
With the use of plastic binders it is inevitable that the binder after the fixation thereof and after the removal of the applied pressing tools will expand somewhat under the influence of the resilient expansion forces in the compressed material in the constriction area. Normally this will be acceptable, because it has been found that the high degree of sealing as having been achieved by the applied high clamping pressure will remain unchanging high even by a considerable pressure relief thereafter.
The fixation of the binder, i.e. the locking of the connector legs to the clamping beams, should be effected such that no significant return movement will occur after the relief of the clamping tool pressure. According to the above, however, a certain small amount of return movement may be acceptable anyway, which may largely facilitate the designing of well suited binders.
For achieving a perfect sealing of or in the constriction area it will normally be necessary to compress the material by some 10-50% all according to the cross sectional shape of the area and the E-module of the particular plastic sheet material, i.e. a quite considerable axial displacement of the material should be effected for making sure that all kinds of axial leaks have been sealed off. Particularly with the use of sheet materials of a low E-module it may be disadvantageous for the integrity of the material to use a strongly binding ring member of small "height", i.e. of a small axial dimension, because the outermost material in the constriction area may then burst by the forceful clamping together of the correspondingly thin clamping beams of the binder. Ideally for this purpose a rather high or long binder should be used, which will distribute the pressure over an enlarged outer area of the constriction and thus be more lenient to the sheet material. This material should still be clamped sufficiently for an overall expansion in the axial direction, but with the use of a relatively long binder the axial expansion will be smoothened out and be partly suppressed in that the expansion forces will be taken up by counterresilient forces from the material portions frictionally held by the binder adjacent the axial end portions thereof.
However, such long binders will be correspondingly expensive, and for the invention it is an important recognition that a corresponding result will be obtainable with the use of "short" binders, viz. by a suitable design of the tools used for the clamping actuation of the binders. Thus, this desired effect will be achievable by externally holding the material of the constriction area just outside the binding area in such a manner that the held material cannot be freely axially displaced, this being effectable by means of special clamping tool portions, which, in conjunction with the clamping together of the binder, will clamp against the constricted material area just outside the opposed ends of the binder. Hereby there is provided a frictional resistance against the axial expansion of the material, what will correspond to an increase of the E-module in the actual binding area, such that high clamping forces may be applied to a "short" binder without the material being damaged. When the clamping pressure is relieved and the clamping tool portions are removed the binding pressure may cause a certain post-expansion, but as already mentioned it will be unimportant whether an associated pressure reduction inside the bound area will occur, when it has only previously been ensured that a real compaction and axial displacement of all sub portions of the material in the binding area has been obtained.
It is important that the binder opening is beforehand disposed approximately in accordance with the cross sectional shape of the constriction area, such that the casing material by its compaction between the clamping beams shall not have to be widely laterally deformed in order to engage the cross leg connection between the clamping beams.